The present invention relates to a manufacturing method of a clutch for an automatic transmission which comprises two clutches to conduct connection/disconnection between of an input shaft and rotational elements of a transmission mechanism, and the automatic transmission equipped with such two clutches.
Conventionally, an automatic transmission, in which two clutches are provided on an input side of a transmission mechanism including plural planetary gears and a power transmission path of an input rotation to the transmission mechanism is selectively changed by these clutches to provide multistage shifts of the transmission, is known as an automatic transmission for automotive vehicles. Herein, respective input members (drum members) of the two clutches are connected to the input shaft. For example, according to the automatic transmission which is shown in FIG. 11 of Japanese Patent Laid-Open Publication No. 2007-78191, an inner peripheral portion of a drum member of one of clutches is welded to a flange portion of an input shaft, and to this drum member is coupled an inner peripheral portion of a drum member of the other of the clutches via a spline connection, thereby connecting the two clutches to the input shaft.
There are other types of automatic transmission in which the connection of the drum members of the two clutch members and the input shaft is conducted by connecting the inner peripheral portions of the drum members of the clutches to a sleeve member which is coupled to the input shaft via the spline connection by means of welding or spline connection.
Herein, in case the drum member of at least one of the clutches is coupled to the sleeve member via the spline connection, the spline connection may require a specified length in its axial direction. Accordingly, the sleeve member may be relatively long, so the entire length of the automatic transmission in the axial direction may become improperly long.
The connection with the electric welding between the drum members of the two clutches and the sleeve member may be considered as one of countermeasures for this problem. Herein, various elements of the clutch, such as a piston, a return spring, a spring receiver (a seal plate to form a centrifugal balance oil-pressure chamber), are provided between the drum members of the two clutches, so the electric-welding connection of the two drum members needs to be conducted via these various elements. Accordingly, the drum member of one of the clutches is welded to a specified position of the sleeve member, then the drum member of the other clutch is made contact the specified position of the sleeve member in a state in which the piston, spring and so on are disposed properly between the drum members. Here, in this state, an electric current is applied to the drum member of the other clutch and the sleeve member. Thus, the electric current flows through not only the contact portion between the drum member of one of the clutches and the sleeve member but the piston, spring, drum member of the other clutch, and so on. Accordingly, there is a possibility that welding would occur at a portion between the spring and the piston as well as the contact portion between the drum member of one of the clutches and the sleeve member. Further, there is a possibility that the piston, spring and the like have a welding deformation.